The present invention relates to a distributed network computing system for connecting a plurality of terminals and, more particularly, to a distributed network computing system for providing an application service such as an inventory control service to various terminals such as PDAs, personal computers, and portable PCs having different processing capabilities and connected to a plurality of communication networks including a public network, a wired LAN (Local Area Network), and a wireless LAN, and a data exchange apparatus and method and a storage medium used in this system.
The mainstream of conventional data processing using computers is a centralized processing system in which a plurality of terminals are connected to one main computer. Inversely, in a distributed processing system, a plurality of computers are connected to form a network such that the computers can share their resources to perform efficient processing. An environment for allowing distributed processing of an application among machines of different types is called a distributed computing environment.
In a network environment where distributed computing is realized, the user need not be aware of the place of a program or data. Logically, since the entire network behaves as if it were one computer, the user can utilize desired data or function in the self operation environment.
Assume a system for providing an application service such as an inventory control service to each terminal in the above-described network. The user terminals have different processing capabilities (the capability is called a terminal attribute, including not only the capability of the CPU but also the display screen size and the memory capacity). To absorb the difference, a manual data operation must be performed on the terminal side or on the server side.
Each terminal is connected to, e.g., a public network or a wired or wireless LAN. That is, these terminals use different communication networks. Therefore, the data transmission rate, the transmission volume, and the quality change relative to each other in units of communication networks as communication infrastructures.
Generally, assuming that a personal computer as a general-purpose device has a high-level processing capability, a PDA has an intermediate-level processing capability, and other terminals have a low-level processing capability. As for the communication infrastructures, the transmission volume and quality of a wired or wireless LAN are at a high level. Those of an ISDN (Integrated Services Digital Network) are at an intermediate level, and those of an analog wired network, or an analog or digital wireless network are at a low level.
In the network environment, the processing capability changes in units of terminals, and the communication capability changes in units of communication infrastructures. Therefore, it is very difficult to commonly provide an application service to various terminals in such an environment.
Generally, the attribute of each terminal used in the system is determined at the time of system designing, and the application service is provided in accordance with the attribute. For this reason, even when a terminal having a new attribute has been developed, the terminal can hardly be introduced into the system and used.
To provide a service while absorbing the difference in processing capability among the terminals or the difference in communication capability among the communication infrastructures, cumbersome processing must be performed. Accordingly, a large server computer having an adequate capability is required.
An establishment such as a company or a factory must be equipped with an exchange system for performing exchange/connection between extension telephones and between an extension telephone and a subscriber telephone line (main wire). Generally, a private exchange system or private exchange equipment is referred to as a PBX (Private Branch exchange) and, particularly, a digital private exchange system is called a digital PBX. The digital PBX converts a speech signal into a digital signal and processes the digital signal. When OA devices such as a personal computer, a wordprocessor, and other computers used in the office are connected to the digital PBX, data and speech signals can be uniquely and efficiently processed. In addition, when various network functions are added to the digital PBX, a wide area network can be constituted from an intra office communication network.
When a LAN is constituted for the first time, several computing devices are connected to one Ethernet cable (coaxial cable) in many cases. However, as the network expands and the number of connected devices increases, the physical length of the cable reaches the limit. As a means for physically and logically expanding the network beyond the limit of the cable, a router or the like is used.
The router can constitute a network having a closed loop. The router determines an optimum route (routing) and passes only necessary packets therethrough. The router determines the route in accordance with a network number in an internet protocol (network layer) and then in accordance with a node number, and determines the final destination.
Since the internet protocol in the network layer is defined in units of protocols including TCP/IP and OSI, the router basically supports one protocol. In other words, the router can select only a network corresponding to a specific protocol from backbone networks with a plurality of protocols. For this reason, the router can be effectively used to meet a requirement for a decrease in load factor from the Ethernet to the line due to the speed.
Conventionally, however, no system has been proposed yet to provide the service while absorbing the difference in processing capability among the terminals or the difference in communication capability among the communication infrastructures on a network connection apparatus such as an exchange system or a router.
On the other hand, a system for managing a large quantity of data is necessary. In the WWW (World Wide Web) which is becoming popular on the internet, a structuring language (tag language) called HTML (Hyper Text Markup Language) is used. As a structuring language other than HTML, SGML (Standard Generalized Markup Language) may be widely used along with the popularization of CALS (Continuous Acquisition and Lifecycle Support).
To display a document formed in the structuring language, a function (browser) of analyzing and displaying the structuring language is required on the terminal side. In other words, data described in the structuring language cannot be provided to a terminal without the browser function.
When data described in the structuring language is directly transmitted on the network, a large quantity of data is transmitted even through a line having a low transmission capability, and this transmission takes a long time. These problems also apply to a component data format such as OLE (Object Linking and Embedding) in addition to HTML.